1. Field of the Invention
The present invention relates to an electric shaver and more particularly to a rotary type electric shaver that cuts whiskers by means of an inner cutter that rotates along an outer cutter.
2. Prior Art
FIG. 6 shows a conventional electric shaver, and it particularly shows the structure of the outer cutter and the inner cutter that makes sliding contact with the outer cutter disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) No. 11-4980.
In this structure, the outer cutter 102 has an outer surface that contacts the skin during shaving. The outer surface is a ring shaped shaving surface 103. The surface that makes sliding contact with a cutter body 107 of the inner cutter 106 on the inner surface of the outer cutter 102 makes an outer cutter surface 104. A plurality of cutter bodies 107 that make sliding contact with the outer cutter surface 104 are provided on the inner cutter 106. Each of the tip end surfaces of the cutter bodies 107 makes an inner cutter surface 108. The outer cutter surface 104 is in a planar shape (or is flat), and the inner cutter surface 108 that makes sliding contact with the outer cutter surface 104 is likewise in a planar shape (or is flat).
The inner cutter 106 is connected to an inner cutter drive shaft 109 via an inner cutter supporting body 118 and is rotationally driven by the inner cutter drive shaft 109. The inner cutter supporting body 118 that engages with a tip end of the inner cutter drive shaft 109 is disposed so as to be tiltable in any desired direction with respect to the inner cutter drive shaft 109.
The inner cutter drive shaft 109 is disposed so that the inner cutter 106 is constantly urged by a biasing means (not shown in the drawings) in the direction that causes this inner cutter 106 to be pressed against the outer cutter 102, i.e., in the outward direction (or upward direction in FIG. 6). As a result of the urging force of the inner cutter drive shaft 109, the flange 102a of the outer cutter 102 contacts the inner wall surface of a cutter frame 28 via the inner cutter 106 so that the outer cutter 102 tilts with respect to the cutter frame 28. The inner cutter 106 that makes sliding contact with the outer cutter surface of the outer cutter 102 is provided so that the inner cutter 106 tilts in accordance with the outer cutter 102.
The area surrounded by the ring-shaped shaving surface 103 of the outer cutter 102 is a recessed portion 112. An outer cutter cover 116 is fitted into this recessed portion 112 so that the outer cutter cover 116 is set in the center of the ring-shaped shaving surface 103. The outer cutter cover 116 is fastened in place by inserting the engaging wall 116a of the outer cutter cover 116 into the engaging hole 112a formed in the recessed portion 112 of the outer cutter 102. The engaging wall 116a is in a cylinder shape that opens at the bottom on the inner cutter supporting body 118 side of the outer cutter cover 116. A recess 116b is formed in the engaging wall 116a and is positioned in the center of the outer cutter 102, and a guide portion 118c which protrudes from the projecting portion 118a of the inner cutter supporting body 118 is inserted into this recess 116b. 
The guide portion 118c of the rotating inner cutter supporting body 118 is supported coaxially with the outer cutter 102 as a result of the outside surface of the guide portion 118c constantly contacting with the inside surface of the recess 116b of the outer cutter cover 116. As a result, the outer cutter 102 and the inner cutter supporting body 118 that supports the inner cutter 106 are kept coaxial; and even when the outer cutter 102 tilts, axial deviation between the outer cutter 102 and the inner cutter supporting body 118 is prevented.
Another conventional outer and inner cutter structure of an electric shaver is shown in FIG. 7 as disclosed in, for example, Japanese Patent Application Laid-Open (Kokai) No. 7-185149.
In this electric shaver as well, the outer cutter 120 and the inner cutter 124 are provided so that these cutters tilt with respect to the cutter frame 123, and the outer cutter surface 128 and inner cutter surface 130 are formed in a planar shape (or they are flat). Unlike the electric shaver shown in FIG. 6, a bearing portion that guides an inner cutter supporting body coaxially with the outer cutter is not provided in the shaver of FIG. 7. Instead, the inside region 122 of the shaving surface 121 of the outer cutter 120 is simply recessed and has a flat bottom. Furthermore, the upper end surface 126a of the inner cutter supporting body 126 that supports the inner cutter 124 is formed flat, and the undersurface of the recessed portion 122 and the upper end surface 126a of the inner cutter supporting body 126 are disposed so as to be spaced apart from each other.
In this electric shaver, a guide surface 132 is formed on the inner surface of the outer cutter 120 so that the inside surface 136 of the cutter body 125 of the inner cutter 124 makes sliding contact with this guide surface 132. The cutter body 125 of the inner cutter 124 is guided by the guide surface 132 so that the inner cutter 124 rotates without making any axial deviation with respect to the outer cutter 120. Since the inner cutter surface 130 of the inner cutter 124 is constantly pressed against the outer cutter 120, the inner cutter 124 conforms to the outer cutter 120 when the outer cutter 120 tilts, so that the inner cutter 124 rotates without any axial deviation.
However, in the electric shaver shown in FIG. 6, when the inner cutter 106 rotates, a load is applied to the driving force that rotates the inner cutter supporting body 118 as a result of the friction that generates between the inside surface of the recess 116b of the outer cutter cover 116 and the outside surface of the guide portion 118c of the inner cutter supporting body 118, and as a result, the electric power consumed by the electric shaver increases. Furthermore, the recess 116b of the outer cutter cover 116 and the guide portion 118c of the inner cutter supporting body 118 need to be manufactured precisely in order to prevent axial deviation of the inner cutter 106.
Furthermore, in the electric shaver shown in FIG. 7, friction occurs by the sliding contact of the side surface 136 of the rotating inner cutter 124 with the guide surface 132 of the outer cutter 120, so that the electric power consumption increases by this frictional force as in the case of the electric shaver of FIG. 6. The electric shaver of FIG. 7 has further problems. Since the side surface 136 of the cutter body 125 and the guide surface 132 of the outer cutter 120 constantly make sliding contact, the side surface 136 of the cutter body 125 can easily wear out, deteriorating the function to prevent axial deviation.